This invention relates to mobile vehicle automatic transmissions, transmission shifters, and vehicle communication sub-systems. The communication sub-system makes use of existing industry standard or proprietary communication protocols and communication spines replacing separate hard wired circuits for ensuring that the shifter is not moved out of a park position without the application of service brakes. Such vehicles appropriate for such installation include but are not limited to light, medium, and heavy-duty trucks and buses.
Many transmission shifters have a position labeled xe2x80x9cParkxe2x80x9d or labeled with some abbreviation of xe2x80x9cparkxe2x80x9d or similar word that is meant to operate some device to halt the vehicle""s forward and reverse motion. The driveline of a vehicle transmits power first from the engine and eventually to the wheels and road. Some transmissions have a built in xe2x80x9cpark pawlxe2x80x9d that locks the driveline through a ratchet-like mechanism, while other transmissions have a device that automatically actuates the vehicle""s park brake. In either case, an injury could potentially occur if the transmission is shifted out of this park position to free the transmission or release the park brake without some other means of impeding the vehicle""s forward or reverse progress.
One way to avoid sudden, perhaps unexpected, vehicle movement is to disallow the operator to shift the transmission out of this xe2x80x9cparkxe2x80x9d position until the service brakes have been applied. U.S. Pat. No. 5,853,348 owned by the same assignee as this invention provided such a system. This prior art system was for selectively locking a steering-column-mounted transmission shifter in a park position that places the transmission in one of two neutral positions. An electrically operated shift lock releasably locked the shifter in park position. The shift lock was under the control of an electric circuit that contained a first and second shift lock relays having normally open contacts connected in series to the shift lock. The electric circuit operatively coupled the relays""coils with the ignition switch, a transmission neutral position-sensing switch, and a service brake-sensing switch. When the service brakes were applied and the ignition switch was on, the shift lock was operated to release the shifter, allowing the shifter to be moved to other positions. This system while effective involved complexity with the two separate relays and two sensing switches.
One issue with mobile vehicle electronics is managing communication between on-board controllers or electrical agents. At a simple level, communication between two electrical agents may be kept physically separated from communications occurring among other agents. Where two or more signals do not use the same physical space, there is no need to separate the signals in time or in carrier wave frequency. Such a communications regime is sometimes termed as physical division multiplexing although the term multiplexing is usually reserved to techniques for applying multiple signals to a single medium or physical space. So-called physical division multiplexing describes how motor vehicles have been traditionally wired. The use of separate dedicated wires to connect each switch and lamp is a type of physical division multiplexing. Obviously, physical division multiplexing, while simple in concept, results in the use of many wires (the classical motor vehicle electrical harness), which are difficult to install during manufacturing and problematic to maintain in the field.
Arrangements allowing a number of agents to communicate over a common physical layer or medium offer much greater physical simplicity. Intelligible communication between two or more devices among a greater plurality of devices, all over a common medium, depends upon the communicating devices being able to distinguish, and understand, messages directed to them from other messages which they receive, but which are not intended for them. The process of distinguishing messages depends upon the transmitter of the message applying some attribute to the message that identifies it to the intended recipient. In human conversation, most people readily distinguish speech directed to them from interfering cross talk in a crowd by the distinctive aspects of the voice of the person addressing them. Where the members of the group are electrical components, the problem still involves identification of a distinguishing attribute of the signal. Appropriate attributes for signals take a number of forms.
A line communicating a signal from a remote switch to a lamp to turn on or off (by having a second switch, local to the lamp, change states to control connection of the lamp between a power bus and ground) cycles only rarely. In a typical trip such a change in state occurs only once or twice, if at all. Where such a line is not intended to provide power to the lamp, and simply indicates changes in state for the local switch controlling the lamp, the line will have the capacity to handle far more data than the occasional indications to turn a lamp on and off. The objective of maintaining simplicity in manufacturing and maintenance are preferably met by allowing communication among a number of components to occur in a single medium, or at least as few communication lines as possible. The line used to connect switch and lamp could interconnect a number of components, carrying messages between any groupings of elements connected to the line when not required to carry an instruction to a lamp to turn on. One way of achieving this objective is a communications regime that divides time into slots during which particular combinations of components have use of a signaling line. Such methods are well known in the art and are examples of time division multiplexing (TDM). In motor vehicles, time division and related multiplexing techniques offer substantial simplification in physical layer required to support the control of vehicle vocations.
Rigid time division multiplexed communications appear to interleave data signals into a single serial signal over a single physical medium. Multiplexed communication systems also provide the reverse function (de-multiplexing) of dividing the single signal into multiple, non-synchronous digital signals. Where demands on the capacity of the data transmission medium are not especially heavy, any unit may be allowed to claim the medium provided collision detection is provided for and other indicia, such as address headers, indicate the signal""s destination.
As applied to motor vehicles, multiplexed communications over serial data paths are an effective technique for reducing the number of dedicated communication paths between the numerous switches, sensors, devices and gauges installed on the vehicles. With each increase in the number and variety of accessories and functions installed on each vehicle, the benefits of using a single, multiplexed communication serial link for passing instructions to and receiving information from vehicle devices as diverse as running lights and rear axle temperature sensors becomes greater. Multiplexing the signals to and from local controllers and switches for vehicle systems promises greater physical simplicity through displacing much of the vehicle wiring harness, reducing manufacturing costs, facilitating vehicle electrical load management, and enhancing system reliability.
The specific manner of implementing multiplexed communications is outside the scope of the present invention, which applies a defined protocol such as the SAE J1939 protocol. Additionally, proprietary protocols may be used although over a network similar to as described here. The development by the Society of Automotive Engineers of the J1939 series of standards for multiplexed communications testifies to the progress in the application of multiplexed communications to vehicles. Standards have been or are being developed relating the communication path, transmission collision detection, diagnostic ports and data protocols, among other topics. The J1939 protocol provides an open protocol and definition of the performance requirements of the medium of the physical layer, but also allows for development of proprietary protocols. The SAE J1939 protocol is a specialized application of a controlled area network (CAN) and may be readily implemented utilizing commercial integrated circuits such as the C167 Integrated Circuit from Siemens of Germany.
A serial communications system utilizing a multiplexing regime can link several remote digital controllers positioned around a vehicle with an electrical system controller or electronic system controller (ESC) for two-way communication. Remote digital controllers are addressable, allowing them to respond to signals intended for them initialize particular functions. The transmission ECM may be a remote digital controller. They may also include programming that allows the device to react to local conditions as well as condition indicating signals provided the controller. The ESC may pass requests and instructions received for operations of certain devices, addressed to the correct remote controller, in a fashion to condition the timing and duration of the responses to requests to better manage overall vehicle electrical load.
What is needed and does not exist in the prior art is an improved park position locking system for an automatic transmission shifter or a vehicle with such a system that disallows the operator from shift the transmission out of a xe2x80x9cparkxe2x80x9d position until the service brakes have been applied and manages this interlock over a multiplexed communication network or backbone without the need for separate relays and sensors.
An object of the invention is to provide an improved park position locking system for an automatic transmission shifter or a vehicle with such a system that disallows the operator from shift the transmission out of a xe2x80x9cparkxe2x80x9d position until the service brakes have been applied and manages this interlock over a multiplexed communication network or backbone without the need for separate relays and sensors. This should at a minimum save on the cost and complexity of having the separate relays and sensors. A second object of the invention is to provide for communications between the gearshift and the electronic transmission without the need for a dedicated electrical communication line.
The transmission and gearshift communication sub-system and vehicle with the subsystem installed of this invention satisfies all the objects of the invention and others not mentioned. Rather than have separate relays and sensors for ensuring that an operator can not move a shifter out of a a PARK position without applying service brakes, the communication subsystem of this invention involves electrically connecting both the gearshift, the ESC, and the transmission ECM to a common vehicle network. The ESC or the network will include a sensor for brake pedal position. The network may allow communication by an industry standard, such as J1939, or by a proprietary protocol. The key point is that the ESC, the gearshift, and transmission ECM are both tied into a common network to communicate using a standard protocol and that the ESC is programmed to query the status of the brake pedal, query the status of the transmission, and finding the brake pedal depressed and the transmission in PARK, the ESC will send a signal to activate a solenoid in the gearshift to release a Park position locking mechanism to allow the operator to move the gear shifter out of a Park position. Otherwise the ESC will provide signal to the solenoid in the gearshift to continue to engage the Park position locking mechanism. These queries and signals will be under a standard multiplexing protocol. There may be other digital controllers engaged to the network for communication. No special relays or dedicated line between the gearshift and the transmission will be required.
Additional effects, features and advantages will be apparent in the written description that follows.